Video data is generally processed and transferred in the form of bit streams. Variable Bit Rate (“VBR”) video encoders can achieve better quality video compression than Constant Bit Rate (“CBR”) video encoders for the same average bitrate as measured over a relatively long time interval, such as, for example, over an entire program length. VBR encoded video is sometimes called Constant Quality video. This is due to the fact that as the complexity of the video changes throughout the video sequence, variable bit rate encoded video is created to maintain a constant quality. CBR video encoders are typically used to meet the bandwidth requirements of a network traffic model.
VBR video is generally used for applications that do not use fixed bandwidth channels. VBR video may be used for DVDs, for example. Unfortunately, communications networks typically have fixed bandwidth links that are more amenable to CBR video. In CBR video, the encoded bitrate is kept constant, which causes the perceived video quality to vary. This leads to a worse user experience than for VBR video, because the worst case video quality for CBR is generally worse than the constant quality level for VBR, and user perception is greatly influenced by the worse case quality.